Can you go back to Astrodienst, and on the chart construction page (a bit lower down) input Ceres and Black Moon Lilith? One or both might be implicated in the symptoms you described. Ceres is a dwarf planet/asteroid named for the goddess of agriculture who sometimes shows up in eating disorders. [Do you know if your sister is bulemic?] BML is kind of a spoiler, or the "inner bad girl" in the chart.
But just looking at what we have so far, it is interesting that your sister is a dancer, as the 12th house rules the feet. The moon indicates how we simply "feel" things emotionally (such as music) while Jupiter is usually a good luck factor. Your sister has these planets wired into a "kite" formation, with sun-Venus at the tip of her kite. The sun is one's identy, and Venus rules the fine and performing arts!
It is not unusual for high school or university seniors to suddenly wig out, because all of a sudden they have to leave their comfort zone and jump into the unknown. These stresses, if not articulated openly, can lead to nervous disorders affecting the stomach.
Currently your sister has transiting Neptune and Chiron in her 6th house of health, opposing her moon Jupiter. Each planet has multiple meanings, and the moon also rules the stomach. Neptune suggests illnesses that are hard to diagnose, as well as drugs; and Chiron shows us "where it hurts." Ideally both of these planets ultimately lead to greater wisdom and compassion, but it can be a challenging time for people when they are in the "hurt" stage, before the wisdom kicks in.
As if this weren't enough, transiting Pluto is opposing your sister's sun. She may feel as though powerful forces or even people are opposing her interests at this time. She may feel an overhwelming desire simply to shut herself up at home, rather than face them.
Natally your sister has Mercury (thinking function) conjunct Chiron and opposite Saturn, a planet that teaches hard work, patience, and deferred gratification if well-used; but that can also lead to pessimistic thinking of not being good-enough if undeveloped. I suspect your sister, at this threshhold time of her life, fears that she will never make it as a dancer, but cannot imagine what else to do.
The moon (emotional needs as well as the stomach) can encourage binge eating, especially of carbs as these act as a sedative.
You are a good sister to be so concerned. You sister needs to take a doctor's note to her teachers and student advisor ASAP, so that she can cget a medical leave or extentions on her courses, vs. failing them.
Then your sister's ally here will be her natal Mars and Pluto, which teach raw courage in the face of adversity. With Pluto trine her sun, she has the capacity to undergo profound personal transformation.
The moon also rules night and sleep, so we see how your sister's symptoms combine in an astrologically understandable way. I suffer from insomnia myself, so I sympathize with her. The best thing is to follow all of the sensible advice out there on how to create a conducive sleeping environment, and then just live with it rather than taking sleeping pills. These are habit forming, and even addictive. It is OK to lie awake, just so long as she can creatively visualize calming images and thoughts, vs. stressing out about not sleeping.
I find I get my best sleep in the early morning hours-- she may too; so ideally she can sleep in a little.
Having no memory of eating in the middle of the night suggests either sleep walking, or some kind of black-out, such as occurs with heavy drinkers who don't recall in the morning what they said the night before. Do you know if she is secretly drinking, or using drugs? The main thing is that if she is sleep walking, you don't want her to accidentally injure herself.
This is a good time for your sister to be under the care of a doctor, and probably a licensed clinical psychologist. If she hasn't discussed these symptoms with her psychiatrist, she should do so soon.